I don't think we're quite back to first principles here Les; in the 1950 before Fitt's List and the term Human Factors were even heard of human interface design was considered 'common sense' and look where that got us.

The main point being missed so far in this thread is that an HMI is not 'designed' in isolation of: the task being undertaken; the 'design' of the Mk 1 Human(s) using the interface and the context of use - these are equally as important as the application of HMI design guidelines (like those of the FAA). A common misunderstanding of engineers and managers is that they can pick up some HMI guidelines and design a good (safe) HMI without taking the people, procedures and other equipment into account all within the often complex and chaotic context of use. In my experience, too many engineers and managers still think that HF and HMI design are common sense and that fact is keeping systems development in the dark ages.

In short, the integration of Human Factors into the systems development life-cycle needs to be undertaken to address task modelling; human cognitive and physical limitations and strengths; environmental factors etc. etc. before the HMI design is even considered. To use your analogy: the HMI guidelines may be the syntax but the Human Factors principles, methods and techniques are the semantics.

>> Henry Ford framed it well (with a metaphor of course): "If I asked them what they wanted they'd tell me, 'faster horses'."
BTW, I can identify with the Henry ford quote, a large military system update I once worked on was based on 1960s technology had an Operational User Group run by operators (not HF experts or engineers) and after many months of deliberation the 'design' they arrived at was to implement exactly the interface they already had but hosted on modern computer workstations.

BTW: A good text book covering both the 'semantics' and 'syntax' is Sanders and McCormick, Human Factors in Engineering and Design, McGraw-Hill, 1992. A good starter book on the general topic of engineers and human factors is: Richard Gabriel, What Engineers and Managers Need to Know About Human Factors, SAE International.

Can we get back to first principles here. A human machine interface (HMI) is just a window into a process that allows human beings to observe what's going on, understand what's going on and manipulate what's going on (when human intervention is required) such that the target system succeeds in its mission (in our case, without killing anyone).

A 'good' HMI therefore supports: observe-ability, understand-ability and control-ability If you like the devil is in the 'ilitys'

After 10 years working with chemical processing reactors of all levels of complexity, sizes, shapes and chemical processing technologies, followed by a further few years working in wide area control systems in the rail industry, interspersed with a year working on development standards for computers in the shutdown loop of nuclear reactors I have concluded the following:

Observe-ability
A groovy HMI (with all the right contrast ratios and menu hierarchies) is useless if you don't have the instrumentation to observe what's going on in the process. Case study: QF32 would not have had an engine explosion if Rolls-Royce did a mass balance around the lubricating oil flow in their jet engines. A mass balance would have revealed an oil leak that ultimately caused the explosion and the near death-experience of 300 odd people.
Further, these days, just the presence of sensors is not enough. You need the computing power to calculate secondary variables such as mass balance and rates of change. It can get even more complicated in chemical processing when the output of chemical analysis equipment requires significant processing to come up with numbers that mean something to human beings. Some of these numbers need to be calculated at high rates depending on the time constants of the target process.
A simple example: in a latex reactor control system I once worked on the most important number in the plant was the rate of change of reactor temperature. It was a lead indicator of trouble, maybe 6 to 8 hours in the future. My point is that the HMI could display this number in the most primitive and clunky way and it would still be a potent tool in man machine interface. The fact that it existed was most important, not the way it was displayed.

Understand-ability
In response to those who might say, "Aw shucks these systems are highly complex these days and operators can easily get confused. Gees look at what happened at Chernobyl and Three Mile Island. " ... I say, "squeeze out the tears you sorry bugger."
Professional control systems engineers have known for years that highly complex systems can be simplified using the right metaphors in design. Cooperating state engines is one good example that is pretty well universally applied. ... Although some industries do go through dark ages where this is forgotten. For example in one project I actually had to fight to universally apply this model across a smoke extraction system. In the end I won by pulling rank and (metaphorically) executing anyone who disagreed with me.
My point is that at the root ball of understand-ability is the ability to understanding system state. And you cannot achieve this without a well thought out design using a state model.
Returning to the latex reactor, in common with every other chemical processing plant I ever worked on, apart from some critical raw or calculated process variables, the next most important set of numbers was the state of each unit operation in the process (we called it the step number – a concept easily understood by anybody). If the controls for these unit operations were implemented with state engines this became a simple matter. Some operations (the ones that were potentially explosive) were more critical than others. So you could walk into a control room look at a couple of numbers and very quickly get the complete picture of where the plant was up to, or if it was, in fact, in a dangerous state. It was observe-ability heaven!
Once again, the display of these numbers could be as clunky as you like the fact that they existed was the important thing. And they would not have existed without a design totally focused on understand-ability through human friendly metaphors.

Control-ability
Once again a groovy HMI is useless unless you have the final control elements to actually control the process. In chemical processing this took a massive leap of faith as large sums of money had to be spent on installing elements such as control valves that could be manipulated by a computer. It got so expensive that 30 percent of plant capital went into instrumentation and final control equipments. Just the act of running a pipe down off a pipe rack and installing a control valve with all its associated block and bleed equipment could cost upwards of 20,000 dollars (in the 1970s).
Another thing I noticed about controllability is that the less control you give to a human being the better of you are. I experienced some plants that could not be manually controlled by human beings. One tubular reactor a colleague worked on could only be controlled by a computer algorithm. If the algorithm or the field equipment looked like it was failing they would shut the plant down.
Here's the interesting thing: once you're committed to proper instrumentation and final control elements, computers, and state engine models you tend to take it all the way and make automation total. Google and friends have reached this conclusion with the automobile. The less our hands touch the steering wheel the better off we all will be. (I invoke a previous post, the aphorism from Apocalypse Now: never get out of the boat, absolutely god damn right, unless you're prepared to take it all the way. No matter what happens.) One downside of total control is that operators need to understand what is going on in the rare situations where they need to intervene. I am told that the most common explicative in an aircraft cockpit is, "What the f... is it doing now?" Once again this is where good metaphors in design play a critical role.

A note on engineers not understanding user needs.
In my experience this was solved by chemical plant engineers actually writing the control software after appropriate training in control theory and the target computer control systems. Plant engineers were then responsible for maintaining their own software. Unfortunately this is impractical in other domains such as aviation.
I will say one thing though, understanding fundamentals of any process, chemical or nuclear, is one thing but knowing how to control it safely is another. In operating any process you need to look at it from the point of view of set points, measured variables, lead and lag indicators, time constants, dead time, gains and rates of change. I found this perspective missing in a lot of plant engineers, that is before they were properly trained in control theory. Some of them seemed helpless to solve their process problems purely because they were looking at the issue through the eyes of a control Systems engineer. Indeed Chernobyl was a result of some punter not understanding that running those reactors at low power created an unstable system which got out of control and ran away when they attempted to control it manually (just like the tubular reactor I mentioned above).
There is also a dilemma here which I experienced many years ago when it fell to me to train operators in technologies and ways of operating that they could not possibly visualise with their current experience. Henry Ford framed it well (with a metaphor of course): "If I asked them what they wanted they'd tell me, 'faster horses'."
There is an element of this in many new things we design these days. For example Steve jobs never had focus groups. Page, Brin and Musk at some point in their careers were all viewed as crazy (Musk once asked his latest biographer, "Am I crazy" as if he was unsure himself).

Steve
I had a quick flip through the FAA Human Factors Design Guide. All good stuff but I noted that none of the above issues were addressed. It's like I was reading the syntax manual with the bit on semantics missing. Was all that stuff in another chapter? Tell me it was mate or are we entering another dark age.

> The answer is yes, but one of the problems is that engineers are not normally users, so they have a different perspective on what short-cuts or ‘misuse’ might happen. This means that the end user needs to be engaged in the design process too but from my perspective, they aren’t normally that bothered because they can’t see or touch it. In addition, we sometimes get into the ‘but why would anyone do it that way, I designed it this way!’ discussion!

I do not want to hijack the seriousness of the conversation but that reminded me of this: